A significant reason for death and long-term disability due to head injuries and pathologic conditions is an elevation in the intracranial pressure (ICP) due to vascular compromise and secondary sequelae causing edema. ICP measurements before and after injury in a completely closed-head environment have a significant research value, particularly in the acute postinjury period. With current technology, a tethered fiberoptic probe penetrates the brain and therefore can only remain implanted for relatively short time periods. Use of the probe also can cause complications such as infection and hemorrhage and prohibit immediate (at the time of injury) and long-term measurements of ICP. A small, fully embedded, wireless ICP device may simplify clinical management and research protocols by offering a means for semi-invasive and long-term ICP measurement following brain injury. In this chapter, a new digital wireless ICP (DICP) device is described. The dynamic ICP measurement performances of both the analog ICP (AICP) devices (described in Chapter 2) and the DICP devices are evaluated in a specific traumatic brain injury (TBI) (swine) model of closed-head rotational injury.
In Chapter 2, a prototype of an AICP device operating in the industrial-scientific-medical (ISM) band at 2.4 GHz was described that successfully simplified the surgical procedure by reducing the infection rate, the risk of hemorrhage, and the degree of tissue injury.
The AICP device was implanted in a canine model only for a static test, and hypo- and hyperventilation were used to affect variations in ICP. Dynamic ICP variations as a result of TBI in a completely closed-head environment are of paramount importance for understanding the development of a prolonged postconcussion syndrome and facilitating institution of the correct treatment at different stages, particularly in the acute postinjury period. Currently, in experimental (animal) models of TBI, a tethered fiberoptic probe (if inserted before the injury) has to be removed before an injury is induced in order to avoid significant focal damage at the point of probe insertion. Moreover, reinsertion of the probe is possible only after the animal's vital signs have stabilized. However, the act of breaching the cranium after the injury affects the fidelity of the ICP measurements. In addition, proposed noninvasive ICP (NICP) solutions, such as the pulsatility index method based on the use of trancranial Doppler, argued by Figaji et al. , have been shown to be insufficient for accurate ICP estimation.
Intracranial pressure (ICP) monitoring is a significant tool that aids in the management of neurologic disorders such as hydrocephalus, head trauma, tumors, colloid cysts, and cerebral hematomas. ICP is the pressure exerted on the rigid, bony skull by its constituents, which are brain, cerebrospinal fluid (CSF), and cerebral blood. Increased ICP can lead to brain damage, disability, and death. Various modalities have been developed for monitoring ICP in hospitals and in ambulatory conditions. Currently, only catheter-based systems have made it to clinical practice. The catheter-based systems can only be used in a hospital setting and have a limited useful life owing to drift and the risk of infection. The wired methods of patient monitoring are cumbersome, cause patient discomfort, and can potentially introduce motion artifacts in the measured quantity. The contemporary medical world is witnessing a transition from a wired to a wireless healthcare domain.
Wireless Technology in Medical Use
The application of wireless technology in healthcare is becoming ubiquitous, if it is not already so. The therapeutic and diagnostic applications of radiofrequency (RF) and microwave technologies in medicine have been the subject of extensive study in the past [1–3]. Medical implants for the transfer of information at these nonionizing frequencies have been developed . Research accomplishments using data communication links at microwave frequencies between a medical implant and an external unit have been reported by many researchers. The resonance characteristics of implanted antennas operating at a frequency band of 402 to 405 MHz and their radiation pattern outside the body have been shown to be favorable for short-range medical implants . Poon et al.  demonstrated that the optimal frequency for power transmission in biologic media is in the gigahertz range. Gosalia et al.  demonstrated a novel approach of establishing a data telemetry link between an implant and an external unit in the 1.45 and 2.45 GHz band for retinal prostheses. Such medical implants are basic components for the success of telemedicine, which refers to the use of telecommunication technologies in healthcare. Telemedicine not only facilitates medical treatment and care but is also gaining popularity in posthospital patient care . It provides expert consultation in remote understaffed locations and advanced emergency care via modern telecommunication techniques . Mobile patient monitoring systems using wireless implants have been developed to maintain records of patient vital signs and history [10,11].
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